The invention relates to a method and an apparatus for uphill casting/low-pressure casting, especially of light metal alloys, with an underlying casting furnace having a riser pipe and a mouth opening of the riser pipe and having a mould with an underlying pouring-in opening and having a slide valve closure for the pouring-in opening, forming a flow-through channel which for casting takes on a substantially straight, longitudinal course of especially uniform cross-section.
Compared with gravity casting, uphill casting has the substantial advantage of a smooth controlled casting process. By this means the entrance of air bubbles and oxidation skin which is associated with any turbulence of the melt during casting is avoided. When using core packages as moulds, the separation and entrainment of moulding material in the gate and in the runner can be avoided which otherwise leads to a deterioration in the quality of the castings.
A disadvantage with uphill casting is that in general it is necessary to wait for the solidification process of up to 15 minutes duration before the mould just filled can be removed and the next mould can be brought over the casting furnace. In order to rectify this disadvantage, it has already been proposed that moulds should be closed directly after the low-pressure casting in the pouring-in opening and removed immediately from the riser pipe.
It is known from CH 415 972 that moulds for low-pressure casting can be provided with an underlying shut-off valve and a feeder head positioned thereover, below the mould cavity. The shut-off valve consists of a slider plate lying inside a pouring-in channel with a flow-through opening which is displaced transversely with respect to the pouring-in channel. The feeder head has a volume-displacing slider piston. Although the feeder head is heatable, after closure of the shut-off valve, there may be some solidification of the melt in the flow-through opening of the slider plate, which requires separate removal of the plug there formed before the next casting process.
DE-AS 2 147 678 discloses an apparatus for uphill casting in which a slider unit is secured to a mould. Here, a slider plate is inserted in the longitudinal course of the flow-through channel so that it sits flush for closure of the flow-through channel. The seal is incomplete.
DE 2 836 434 C2 discloses a three-plate slide valve closure for steel casting vessels which is designed to control the underlying outpouring of such vessels. Here are arranged in a cassette to be attached under the bottom of such vessels, from top to bottom, a base plate, a slide plate and a lower plate which have flow-through openings forming a flow-through channel. In this case, the opening in the lower plate in the direction of motion of the slide plate is approximately twice as large as the openings in the base plate and in the slide plate. The flow-through direction of the melt is continuously falling in this slide-valve closure.